User guide

Quantum Ethernet TCP/IP Modbus Application Protocol
840 USE 115 00 Version 1.0
81
The header is 7 b
y
tes lon
g
, and includes the followin
g
fields:
inv_id[2 b
y
tes] invocation id used for transaction pairin
g
proto_id[2 b
y
tes] used for intra-s
y
stem multiplexin
g
,default is 0 for Modbus
services
len[2 b
y
tes] the len field is a b
y
te count of the remainin
g
fields and
includes the dst_id and data fields.
The remainder of the pdu includes two fields:
dst_idx[1 b
y
te] destination index is used for intra-s
y
stem routin
g
of
packets.
(
currentl
y
not implemented
)
data[n b
y
tes] this is the service portion of the Modbus pdu, mb_pdu, and is
defined below
The service portion of the Modbus Application Protocol, called mb_pdu, contains 2
fields:
mb_pdu ::= { func_code[1], data[n] }
func_code[1 b
y
te] MB function code
data[n b
y
tes] this field is function code dependent and usuall
y
contains
information such as variable references, variable counts, and data offsets.
The size and content of the data field are dependent on the value of the function
code.